There is an interesting blockchain (Mina protocol) which has the property of being constant sized. For this, they use zk-SNARKS (and you can read more there).
However, they still do global consensus, so in this sense, Holochain is still way more preferred.
The reason I bring this up, is because the technology itself can be interesting to reduce the growth of sourcechains (and thus DHT’s).
The use case is only for those DNAs where we only care about a final state and the fact that all ‘transactions’ up until now where ‘correct’. This would correspond to update and delete elements in Holochain. I’m thinking here about lots of tiny transactions, where the data integrity is important, but not the history itself. Would also be useful here: Limiting the size of my 'chain'.
This would be an alternative approach to Throwaway DHT and all linked topics, to reduce storage.
This would need of course extensive support in both core Holochain, but also be possible and ‘activited’ by the developer on the hApp level.
I’m writing this down for the far, far future, when Holochain is settled and will need to start to think about reducing the storage footprint even more (and if throwaway DHTs would turn out too much of a hassle - or not).